Description:
An example of a beneficial ectoparasite is the leech, which is making a comeback in medical circles for its anticoagulant properties and other medicinal uses as related in this article from the BBC News. According to this article, leeches are particularly useful when a patient's blood vessels are too weak to transport blood away from part of the body, causing venous congestion. "Attaching leeches to the body can draw the blood away gradually and painlessly since leech saliva contains an anaesthetic."